Conventionally, as a sheet take-out apparatus for taking out a plurality of sheets in the stacking state one by one on the conveying path, a take-out apparatus for permitting a take-out roller to rotate in contact with sheets at one end in the stacking direction, thereby take out the concerned sheets in the surface direction almost orthogonal to the stacking direction is known (for example, refer to Japanese Patent Application Publication No. 2003-341860). This apparatus, after the sheets at one end in the stacking direction are taken out, moves the plurality of stacked sheets in the stacking direction and supplies the sheets at the end to the take-out position always in contact with the take-out roller. Further, this kind of take-out apparatus, for example, is incorporated into a postal matter processing apparatus for checking and sorting a plurality of postal matter.
The take-out apparatus has a separation structure for separating the second and subsequent sheets following the sheet taken out on the conveying path by the take-out roller. The separation structure includes a feed roller arranged on the same side as the take-out roller for the sheet taken out on the conveying path and on the downstream side of the take-out roller in the conveying direction and a separation roller arranged opposite to the position across the conveying path for the feed roller. When there are no sheets on the conveying path, the separation roller is pressed in the contact state by the feed roller.
The feed roller rotates so as to feed the sheets taken out on the conveying path in the forward direction. On the other hand, the separation roller, when there is one sheet between the feed roller and itself or there are no sheets, follows the feed roller and when a plurality of sheets are taken out on the conveying path in the stacking state and pass between the feed roller and itself, gives separation force in the opposite direction to the take-out direction to the second and subsequent sheets on the separation roller side. By doing this, the second and subsequent sheets are applied with brakes and are separated from the first sheet.
Generally, the aforementioned take-out roller, feed roller, and separation roller are composed of a rubber roller and act frictional force on sheets, thereby give conveying force. Therefore, the frictional force acted on sheets varies with the individual differences between the rollers, wear with time, and soil. Further, depending on the surface condition of each sheet, a slip is caused between the sheet and the rubber rollers. Namely, in a take-out apparatus using the conventional rubber rollers, the sheet take-out, separation, and conveyance cannot be controlled highly precisely to a desired condition.
Particularly in the conventional apparatus aforementioned, the take-out roller is rotated always at a fixed speed, so that between the taken-out sheets, gaps are hardly formed. Further, even when a plurality of sheets are taken out in the stacking state, the sheets separated by the separation force given by the separation roller are immediately started to be conveyed in the normal direction, so that gaps are hardly formed between the sheets. Therefore, in the conventional take-out apparatus aforementioned, the sheets are separated and taken out on the conveying path, and then the conveying speed of the sheets is changed stepwise, thus gaps are formed, though by this method, it is difficult to control the gaps between the sheets to a desired value.
Further, a sheet separation and conveyance apparatus including a double feed detection portion for detecting double feed of stacked sheets which are taken out on the conveying path by the take-out portion, a separation portion for separating a plurality of double-fed sheets, which are detected for double feed by the double feed detection portion, from each other, and a control portion, when double feed is detected by the double feed detection portion, for controlling the take-out portion so as to stop the take-out operation of the sheets by the take-out portion is known (for example, refer to Japanese Patent Application Publication No. 2001-322727). In the Patent Document 2, it is disclosed furthermore that the control portion controls so as to cause a speed difference between the first sheet and the second sheet, thereby form a gap between them, though a concrete measure for increasing or decreasing the gap length is not indicated.
On the other hand, as an apparatus for controlling the conveying gaps between sheets continuously taken out on the conveying path to an appropriate value, an apparatus for averaging measured data of the respective conveying gaps, comparing the mean data with theoretical data (a target value) prepared beforehand, when the mean data is larger than the theoretical data, advancing the sheet take-out timing so as to narrow the conveying gaps, and when the mean data is smaller than the theoretical data, delaying the sheet take-out timing so as to widen the conveying gaps is known (for example, refer to Japanese Patent Application Publication No. 2001-322727). Namely, this apparatus executes feedback control such as, when taking out the sheets, controlling the take-out timing by giving a fixed conveying gap, measuring the conveying gaps between the sheets after taking out the sheets, calculating the mean value thereof, comparing the calculation results with the target value, thereby controlling the sheet take-out timing.
However, by this method, the mean value of the conveying gaps can be converged to the target value, while a short gap occurring suddenly at the time of take-out of sheets cannot be corrected.